Electric lamp assemblies and lamp fixtures, such as reflectors, are commonly keyed to prevent installation of the lamp assembly in a lamp fixture to which it is not properly matched. Keying is necessary because many lamps are similar in appearance and may be installed by unskilled persons, thus increasing the risk of improper installation. For example, vehicle headlamps may be keyed to ensure that lamps with the required characteristics are installed in the headlamp reflector. A keyed lamp base may include one or more projections of prescribed sizes and locations, which engage matching notches in the reflector during installation. When the lamp base does not have the required key configuration, it cannot be installed in the reflector.
In some cases, two or more lamp types may be used in the same or similar fixtures. For example, lamps with different wattages may be used in a vehicle fog lamp reflector. Installation of a lamp with the wrong wattage in the reflector may have adverse consequences. The light output may be inadequate, the life of the lamp may be shortened, or the lamp power source may be overloaded. Thus, the lamp assembly must be keyed to prevent it from being installed in a reflector to which it is not matched.
One approach is to simply provide a lamp base with a different key configuration for each possible lamp that may be used in the reflector. However, this approach is relatively expensive and inconvenient. Lamp bases are typically molded plastic. The initial tooling costs for multiple different lamp base configurations may be prohibitive. In addition, it would be necessary to stock multiple lamp base configurations. It is therefore desirable to provide a lamp base having variable keying for multiple lamp configurations, while overcoming the difficulties of manufacturing and stocking multiple lamp base configurations.